Aperture

One of the three controls on a SLR or bridge camera is the apature; this controls the size of the hole in the lense and therefore controls the amount of light let into the camera.
The aperture affects the Depth of Field; this is the range in the distance of the photograph that appears in focus, everything immediately in front of or behind of the focusing distance begins to lose sharpness and this occurs gradually.
It is measured in F stops, the larger F stops (e.g 2.8) let in the most amount of light but limit the Depth of Field. Whereas the smaller F stops (e.g 8) let in the least amount of light but increse the Depth of Field.
I took these simple photos to demonstrate the effect of changing the aperture:

Aperture

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